Guilt
by iinoyb
Summary: Sans doesn't like to make promises, but he told himself he would never act on the sinful desires his little brother arouses in him. Papyrus doesn't make it easy for him to keep his word. (NSFW, Papyrus/Sans)


**Warnings:** Fontcest (Papyrus/Sans), Ecto-biology, Hand Jobs, Soul Sex

* * *

It's a beautiful day outside, birds are singing, flowers are blooming...

Well, not really. As far as Sans knows, there aren't a lot of birds in the Underground, and those that do live down here, probably don't do so in Snowdin.

No flowers either, despite what his brother sometimes claims. The snowy weather and frozen earth aren't suitable for plant life.

But if there is one things Sans does know for certain...

It's that on days like these, skeletons like him, should be burning in hell.

Or is that too over-dramatic?

As he watches his brother bend forward to adjust one of the snow piles that compose the outer borders of his latest puzzle, Sans decides that: No, he is not being over-dramatic.

Because all he can see is those extremely short bottoms, shifting slightly to reveal even more of a black clad pelvis, and all he can think about is how it would feel to get his hands on those bones.

And that is more than a little not ok.

Because even if his memories are a bit muddled at times, broken apart like when a snowball slams against a wall, fragmented images of unknown machinery and hands with holes in them, Sans is very aware that the person he is having such sinful thoughts about, is in fact, family.

His brother.

His _younger_ brother.

His younger brother, who seems to Sans no less than purity itself. Misguided innocence and obliviousness. Unadulterated positivity and kindness.

Papyrus, who sees nothing but good in other people and the world as a whole.

And all Sans can think about is how delicious it would be to bend him over the nearest flat surface and fuck him senseless.

He doesn't deserve Papyrus as a brother. Doesn't deserve to touch him. Barely deserves to lay eyes on him.

Because Sans is selfish and weak and cynical, and all he could ever do is corrupt him. Taint him.

And he could never allow himself to do that.

No matter how tempting it sometimes was.

Especially now, when there did seem to be suspiciously more bending involved in this particular puzzle as was usual.

Tempting indeed, but Sans can control himself.

Well, maybe he does feel his magic stirring slightly at the sight, soul pulsing irregularly.

Doesn't matter, as long as his brother has got his back to him. His back, and that wonderful behind of his...

Sans thanks god, or whatever deity is up there, for his loose shorts and baggy hoodie, which he is now busy arranging in such a way as to conceal the very impromptu dick his magic has started to form.

So busy in fact, that he doesn't notice Papyrus is trying to get his attention until he's right next to him.

He startles when the other touches his shoulder, such simple psychical contact almost too much for his current predicament.

"W-what? Sorry, bro, I spaced out for a second." He manages, grinning like a maniac and barely able to keep his eye socket from twitching.

Papyrus sighs in a way that conveys more fondness than actual irritation. "I asked if you could take it out and show me?"

Sans makes a sound that is very similar to that of a whimsun you just made eye contact with.

Because either he is going deaf, or Papyrus just asked him to whip out his boner in public.

"The puzzle you found. You did bring it, didn't you?" His younger brother continues patiently, either not noticing his awkward reaction or ignoring it.

Sans proceeds to have a minor aneurysm, disregarding the fact that this is entirely biologically impossible for a skeleton.

Luckily, his hand somehow manages to reach inside his pocket, taking out the slightly crumpled piece of paper.

"Of course, Paps." He blurts, and quickly moves to put the word search on its intended place, without showing it to his brother first.

Again, Papyrus doesn't mention it, and maybe this should be an obvious red-flag for Sans, if he wasn't so concentrated on his own arousal.

"That's enough work for one day. I'm already getting _bone_ tired." He jokes instead, even adding a wink for good measure.

"Really?" Papyrus asks, and there is an unusual edge of skepticism in his voice that does give Sans pause, if only for a second.

Then, Papyrus shrugs and gestures at the now completed array. "I guess it's okay. The great Papyrus already completed all his calibrations for the day!"

He sets of on the road towards town, waiting for Sans to start feeling his legs again and catch up.

* * *

When they're home, Papyrus says he needs to take a shower and immediately heads for their bathroom.

Sans curses at the unfortunateness of it all. While he has no trepidation about... giving himself a hand, while his brother is in the same house, his room is adjacent to the bathroom, and through trial and error, he has found the walls to be less than desirable when it came to muffling sounds.

He would have to wait until Papyrus was done.

In the meantime, Sans plopped down on the couch, turning on the TV and switching channels in an effort to distract himself.

MTT cooking and MMT quiz have reruns on them that Sans can't bother to concentrate on, but MTT musical is broadcasting some kind of new stage play... featuring Mettaton in a dress.

Perfect, that will kill his hard-on for sure.

He wonders about the technicalities of fitting a frilly gown onto a metal rectangle, thoroughly forgetting his earlier strain and Papyrus's uncharacteristic behavior.

Until he hears the water shut off and his brother coming down the stairs again.

Sans glances over, intent on making some kind of sarcastic comment about the show, but ends up doing a double take instead.

Because Papyrus is not wearing his battle armor. He's not wearing much of anything, in fact.

Only the pair of shorts Sans knows for a fact his brother used to sleep in sometimes... and that blasted scarf.

But besides those, it's just a beautiful expanse of delicate white bones, held together by pure magic, and the sight is utterly enticing.

"B-bro, what-" He tries, and Papyrus looks at him slightly, faint orange blush heating up his face.

"My clothes got wet out in the forest." He remarks, but his eye sockets dart slightly to the left as he does so and Sans can just tell his younger brother is lying.

But Papyrus has other clothes. An entire, orderly kept, closet full of them, and Sans is just about to point this out, when the couch dips besides him and the words die in his throat again.

Has their couch always been so small?

"Oh! It's Mettaton's newest show. Why didn't you say it was on, Sans, I haven't seen it yet." Papyrus pouts, as he takes the seat besides him.

Sans doesn't answer. He's too busy staring.

Because darnit if he isn't going to check out the menu, even if he's not allowed to order.

He's just a healthy young adult monster after all... With an unsuitable thirst for his own brother.

Yikes.

Papyrus is close, too close, side flush against his, and Sans can feel the warmth of the other's magic practically radiating off him.

It feels nice, warm, and he slowly relaxes out of his tense stature, leaning slightly against the taller skeleton in turn.

And he can see his little brother smile at the action, so Sans guesses it's alright.

Papyrus is watching the show and Sans is pretending to watch the show while actually watching him.

Admiring the more graceful lines of his younger brother's body, so unlike his own and yet oddly similar.

Like two sides of the same coin, while also entirely different currencies.

And he can feel the other's soul, he can feel it always, no matter where Papyrus is, like they're connected somehow, but now sitting besides him he can feel it burning and his own soul lurches in response.

It is an odd sensation, one that Sans knows is not normal, but it brings him comfort.

Because it means that a piece of his brother is always with him, wherever he goes, and vice versa. It means that they are a part of each other in a way that is undeniable and permanent.

Like two halves of the same being.

So maybe other's would consider it morally wrong of him, to desire his brother the way he does, but right now, when it's just the two of them and the shared warmth between them, Sans revels in a complete feeling of peace.

He could stay like this forever. Just close his eyes and bathe in this sensation until the end of time.

This train of thought is thoroughly derailed by the feeling of Papyrus tracing his hand down his tight, rubbing mindless circles that make the heat return to Sans's cheeks tenfold.

Oh, right. He's sitting on a sofa with his half-naked brother next to him.

If Sans didn't know better he'd think Papyrus is doing this on purpose.

But surely that couldn't be the case.

His baby brother is far too innocent, doesn't know anything about those kinds of things. And even if he did, Sans was sure Papyrus could have whomever he wanted.

There was no reason for him to settle for somebody like Sans. Somebody so imperfect. So broken.

But as the stroking continues, moving ever so slightly to the inside of his thigh, Sans considers the possibility that maybe he _has_ miscalculated.

Maybe Papyrus does know some things...

His brother's hand brushes against his still clothed member and stills in surprise, Papyrus's face breaks out in a bright orange blush but he doesn't move, and in that instant, Sans realizes...

There is no such thing as a coincidence.

He lays a hand over Papyrus's, gently, carefully, as if not to unnerve him, and guides its movements.

Slowly, so his brother can pull away any moment.

But he doesn't...

Now neither skeleton is paying any attention to the show. Sans has half-lidded eyes focused on his lap, as if he can't quite believe what's happening. Papyrus's gaze darts between their hands and Sans's flushed face, an odd expression of wonder on his face.

Sans helps his brothers hand move faster, feeling the member through his shorts and moving up and down in quick, stuttering movements. His hips start bucking along, grinding against the inexperienced hold, small gasping sounds starting to escape unbidden.

Papyrus locks their gazes, eye sockets slightly widened at the sounds Sans is making, and in an impulsive moment Sans gives in, bending forward and pushing his mouth against his brother's.

The instant he feels Papyrus push back, mouth opening slightly and teeth clacking together, Sans cums, wetness soaking his shorts.

He feels it on his hand, and so does Papyrus, cause he let's out a little surprised yelp and pulls back, breaking the contact between them.

Sans follows the movement, practically climbing into his brother's lap and facing him, for once thankful for his smaller size.

He brings their mouths together eagerly, allowing his tongue to slip into the other's still empty mouth.

Papyrus's magic is probably too inexperienced to form any extensions of his soul yet, but there are other ways to have fun.

Like going right to the source of things.

Sans pulls back a bit, leaning his forehead against the other skeleton instead, and moves his hands to slowly starts stroking against the sensitive lower ribs.

"Is this ok?" he questions softly, still unbelieving that this is happening at all.

Papyrus can't answer, too lost in the new sensations and making small pleasured noises, so instead he nods his head eagerly, nuzzling against Sans's collarbone with the movement.

Sans smiles, moving his hands to the inside of his brother's rib cage to stroke the more sensitive bones there. He doesn't want to overwhelm his baby bro, but it's hard to hold back now that this is actually happening.

He just needs to make Papyrus feel good too.

Apparently, he's not doing a shabby job either, if the noises he's making are anything to go by.

Papyrus is always loud, so Sans can't see how he expected him to be any different in bed.

Moans fill the room, as he uses his expert hands to rub at all the right spots that he knows are extra sensitive from experience.

Slowly, he makes his way upwards, until he can feel the comforting warmth of Papyrus's soul, now shining bright with excited magic, against his hands.

He touches it gingerly.

His brother groans loudly and stiffens. Sans can't see his face, still buried in his neck, but he doesn't need to, to know it's a beautiful shade of orange.

It is an amazing feeling, the slight thrumming of a healthy, alive soul in his hands, and Sans holds it gently, reveling in the sensation.

Until Papyrus manages to raise his head and whimpers softly.

"S-Sans, Please-" He moans, trembling ever so slightly.

Sans snaps out of his fascination, coming back to the present and what he's about to do.

He starts moving his fingers, slowly at first, then gradually picking up the pace and pressure, until he is rubbing the bright orange soul ferociously.

Papyrus makes a choked sound, hands clamping around Sans's arms almost painfully.

He doesn't let up, stroking and prodding the slightly soft consistency harder until his brother is little more than a incoherent mess beneath him.

"Ah-AH-Sans... ngh-Something's-" Papyrus tries to stutter out, barely able to make a straight sentence anymore.

"It's ok, Paps." Sans breathes, the sight of his younger brother falling apart like this almost enough to get him excited all over again. "Just let go."

And Papyrus does, body stuttering in Sans's arms, the sounds coming from him the most delicious things he has ever heard.

He keeps stroking the now softer soul, letting up pressure slowly until he feels Papyrus slump into him, thoroughly spent.

Sans pulls his hands back carefully, wrapping them around his brother's body instead, holding him impossibly close, yet somehow still not close enough. Never close enough.

He wants to stay like this forever.

Then Papyrus starts laughing softly, a giddy giggle that makes Sans pull back.

"That took a lot longer than I thought it would." The younger brother mumbles, amusement in his voice as he sees Sans's confused expression.

Then the realization from earlier comes rushing back to the forefront of his minds full force, and Sans sighs wearily.

"Who?" He asks simply, and Papyrus averts his eyes again, flushed face becoming impossible brighter at the tactless question.

"Undyne..."

Of course, Sans should have known...

"But the way she explained it, wasn't quite like we did it..." Papyrus suddenly comments, and there is definitely an edge of curiosity to his tone that fills Sans with apprehension.

"No..." He says slowly, voice a tad higher than he would like it to be. "There are... other ways."

Papyrus perks up in excitement. "Wowie. Maybe you could show them to me later?"

Sans did not know it was possible for anybody to look so innocent and sinful at the same time, and it's his turn to turn blue on the cheeks, bringing his face close to his brother.

"Sure, Paps. Anything for you."

* * *

 **Hooray for the classics.**


End file.
